With the advent of modern computer technology and in particular with its utilization for word and text processing applications, it becomes appropriate to address problems not only for text content but also aesthetic qualities of the composition. One of the prime aesthetic factors that can be addressed using a digital computer based office system is text justification. By justification it is meant that the right margin is kept flush and ragged variations in line length are eliminated.
One of the earliest approaches to this problem evolved a justified right margin by manipulating the space between words and characters such that in the event that the last word in a line does not end within the appropriate tolerance of the right margin, spaces are either added or subtracted to the left of the word to accommodate it on the original line or the word is moved onto the succeeding line of text. Whichever way the word is moved, the objective is to terminate the padding process with the last word of the line within a tolerance (or hot zone) of the right margin.
There are several different algorithms for guiding the system in adding blanks or deleting blanks to achieve justification. However, all of the algorithms to one degree or another end up creating gaps of white space in the paragraphs that are sometimes referred to as "rivers of white". This becomes most noticeable when the addition or subtraction of blanks tends to cluster words closest to the right margin and hence destroys some of the aesthetic quality originally sought by margin justification.
A second method for achieving text justification is through automatic word hyphenation. This implies that if a word cannot be accommodated on a line, the system searches for a proper syllable hyphen break and automatically divides the word between two lines. This method avoids the "rivers of white", but for non-phonetic languages such as English the selection of appropriate hyphen breaks in itself is a major problem. Because of irregularities in the English language, hyphen selection by algorithmic means is highly error prone. One prior art method of hyphen selection looks for particular character pairs or diagrams in the word. A "diagram", as defined by Webster's Third New International Dictionary of the English Language Unabridged (1976), is "a group of two successive letters or other symbols". If one of these diagrams is found, then the hyphen is projected for that location. To avoid or lower the likelihood of an incorrect hyphen, the word is compared to an exception dictionary before the hyphen is inserted. If the word is in the exception dictionary, then the hyphens from that dictionary are used. Otherwise, the projected hyphenation point based on the digrams algorithm is inserted. The method of hyphenation tends to be rather error prone.
A third method for achieving text justification is through use of a completely dictionary driven hyphenation method such as the Apparatus for Automatically Forming Hyphenated Words, U.S. Pat. No. 4,092,729 issued to W. S. Rosenbaum, et al. Rosenbaum, et al discloses a complete dictionary method where along with each word in the dictionary its hyphens are encoded in a very compact form. For those words in the dictionary or conjugates of them, the method supplies absolute reliability. However, words not in the dictionary cannot be hyphenated. The ability to hyphenate with the accuracy of a dictionary and not be limited to only the words encoded in the dictionary, while maintaining high reliability, has not be accomplished by any of the prior art methods.